Means for increasing the effect of static



1938-. P. M. HAFFCK'E MEANS FOR INCREASING THE EFFECT OF STATIC Filed Jun 26, 1936 INVENTOR PHILlP M. HAFFCKE Q. ATTORNEY "having the characteristics shown by curve A,

Patented Dec. 20, 1938 UNITED STATES MEANS FOR INCREASING THE EFFECT OF STATIC PhilipM. Haficke, Washington, D. 0.

Application June 26,

1 Claim.

1936, Serial No. 87,404

(Granted under the act of March 3, 1883, as

amended April 30,

This invention relates to increasing the ratio of the amplitude of an impulse produced by static to the amplitude of a signal wave current received concomitantly with such impulse.

It is the object of this invention to provide a circuit whereby there will be efiected a disproportionate amplification of waves received thereby when the amplitude thereof is above a predetermined value, thereby materially increasing the difference between a signal wave and a static-produced wave to facilitate the suppression of the latter in subsequent stages of the receiving set circuits.

In the drawing:

Fig. 1 is a graph showing the relative amplitudes of a signal wave and a wave due to static in the input circuit andalso their relative magnitudes in the output circuit of a tube;

' 'Fig. 2 shows a conventional circuit for an amplifier tube; and

Fig. 3 shows the circuit of Fig. 2 modified to accomplish the objects of this invention.

Heretofore, it has been the practice to decrease as much as possible the ratio of static to signal, but with certain systems of static sup- I .pression the greater the ratio of static to signal the more effectively will the suppressing system eliminate the undesired static component of the received energy. Therefore, when using a sup- 7 pressing system such as has been mentioned, it is desirable to increase the disparity between the peaks of the signal wave and the staticin the input of the suppressing system, and this is efthan a change in the grid bias in the stage in which this system is to be incorporated. Ordinarily it is preferable to use a tube having variable transconductance (variable mu), such as are known under the trade numbers of 35, 58, and '78. It iswell known that the Eg-Ip curve of such tubes is similar to curve A in Fig. 1, whereas the corresponding curve of a linear amplifier is like 13 in Fig. 1. It is apparent that when a tube Fig. 1, is biased to operate about the point 0 V on the lower knee of the curve the portion of the curve included in a received signal represented by 4 will result in an output wave such as is shown at 5. However, if a static-produced wave having amplitude indicated by 6 in Fig. 1 is received concomitantly therewith, the corresponding output component will be defined by I. It will be noted that the ratio of amplitude I to amplitude 5 is very much greater than is the ratio of amplitude 6 to amplitude 4 and, therefore, the suppression of I will be facilitated in systems of the type above mentioned.

Fig. 2 illustrates a well known circuit for one amplification stage of a radio receiver. The variable mu tube has a cathode 8, control grid 9, screen grid l0, and anode II. The input circuit includes inductance I2 and capacity I3 in parallel and a resistance I4 by-passed by condenser i5. Resistor I6 is in the screen grid circult and by-passcondenser I I is connected between the screen grid I0 and cathode 8.

Fig. 3 shows the circuit of Fig. 2 modified to operate according to the present invention. The principal change is in connecting resistor I8 to the screen grid circuit between resistor I6 and the source of positive potential and to the cathode circuit between capacity I1 and resistor I 4. However, the value of resistor I 4 is preferably changed so that the resistors I 4 and I8 constitute a voltage divider to supply the proper bias to cathode 8 to insure that it is operated about the desired point on the E -I curve. In case the receiving set were originally designed to use a. linear amplifier tube in the chosen stage, such tube should be replaced by a variable mu tube and the resistor I8 added. Where the set uses a variable mu tube in the stage to be changed the resistor I8 may be added or in some cases the value of resistor I4 may be increased to, say, 25,000 ohms or more, even up to one megohm, and the mode of operation herein described will result.

Some overall gain up to the output of this stage will be sacrificed from the standpoint of signal intensity, but the overall gain of strong static impulses will prove to be increased to practically the same amplitude as though the stage still had the usual linear characteristic.

All tubes show the variable mu characteristic to some degree when biased to operate on either the upper or lower knee of the E -I curve, and by careful selection of applied grid voltages they may be'used to serve my present purpose; but those types known as having remote cut-off, or variable mu, have much greater working range at the lower knee of the said curve and are best for use in stages where the input voltages are of screen grid and a source of positive potential,

an input circuit connected to said control grid and including a second resistance connected to said cathode, and a constant third resistance connected to said source of positive potential and to said cathode between said tube and said second resistance, said second and third resistances acting as a voltage divider to apply to said input circuit biasing potentials to amplify disproportionately the higher amplitude peaks as compared with those of lower value.

PHILIP M, HAIE'FCKE. 

